Why don't percentages work CSS

I’m trying to replicate this is in codepen but it doesn’t like me using percentages - is there additional code I should be adding to be able to use percentages in height and width instead of px?

Your code so far


<style>
#box-container {
  background: gray;
  display: flex;
  height: 100%;

}
#box-1 {
  background-color: dodgerblue;
  width: 25%;
  height: 50%;
}

#box-2 {
  background-color: orangered;
  width: 25%;
  height: 50%;
}
#box-3 {
  background-color: violet;
  width: 25%;
  height: 50%;
}
#box-4 {
  background-color: yellow;
  width: 25%;
  height: 50%;
}
#box-5 {
  background-color: green;
  width: 25%;
  height: 50%;
}
#box-6 {
  background-color: black;
  width: 25%;
  height: 50%;
}
</style>

<div id="box-container">
<div id="box-1"></div>
<div id="box-2"></div>
<div id="box-3"></div>
<div id="box-4"></div>
<div id="box-5"></div>
<div id="box-6"></div>
</div>

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.141 Safari/537.36.

Challenge: Use the flex-wrap Property to Wrap a Row or Column

Link to the challenge:

Hi @Jesk!

The error message
" The #box-container element should have the flex-wrap property set to a value of wrap ."

You haven’t added anything here